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Home >> GMC >> 1990 >> Forward Control 6.2 J, Automatic, 400/M40 >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - Tests W/Codes - TBI >> Diagnostic Tests >> Code 35: Idle Speed Error (2.5L) >> System Too Lean
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System Too Lean

If air/fuel ratio is too lean, the idle speed may be either too high (check for vacuum leaks) or too low. Engine speed may vary and disconnecting the IAC may not help. "Scan" and/or digital voltmeter (10 megohm) will read an oxygen sensor output less than 300 mv (.3 volt). Check for low fuel pressure or water in the fuel.